Contour underground mine car

ABSTRACT

An underground mine car is disclosed in which the sides and bottom members are at least partly curved preferably having a radius of curvature from about 6 to about 60 feet for the sides and 10 to 30 feet for the bottom, enabling these members to resist applied forces primarily in tension rather than in flexure according to prior construction. In addition, the curved sides transmit longitudinal loads, such as impact and squeeze, more effectively than flat plate construction of equal cross-sectional area. This enables thinner sections to be utilized, and a reduction in car weight can be obtained. Since the number and extent of the welds is marketly reduced in the construction of the invention, and since such welds are often points of inception of corrosive attack, the structure is less susceptible to corrosion and hence this reduction in thickness and thus weight is permissible. The sides and bottom can be made of substantially the same thickness and thus can be made of a single member. Therefore only one longitudinal joint along the bottom of the car is required resulting in inexpensive fabrication. Only one top chord is required to reinforce the unsupported edges of the curved side members. One or a limited number of transversely extending reinforcing members may be provided, if desired, particularly on long cars.

United States Patent 1 Hammonds et al.

[ 1 Oct. 15,1974

1 1 CONTOUR UNDERGROUND MINE CAR [75] Inventors: James C. Hammonds, St. Charles; Walter E. OLeary, Creve Coeur, both of Mo.

[73] Assignee: ACF Industries, Incorporated, New

York, NY.

22 Filed: Mar. 26, 1973 21 Appl. No.: 344,747

Primary Examiner-M. Henson Wood, .lr. Assistant Examiner-Richard A. Bertsch Attorney, Agent, or Firm-Henry W. Cummings [57] ABSTRACT An underground mine car is disclosed in which the sides and bottom members are at least partly curved preferably having a radius of curvature from about 6 to about 60 feet for the sides and 10 to 30 feet for the bottom, enabling these members to resist applied forces primarily in tension rather than in flexure according to prior construction. In addition, the curved sides transmit longitudinal loads, such as impact and squeeze, more effectively than flat plate construction of equal cross-sectional area. This enables thinner sections to be utilized, and a reduction in car weight can be obtained. Since the number and extent of the welds is marketly reduced in the construction of the invention, and since such welds are often points of inception of corrosive attack, the structure is less susceptible to corrosion and hence this reduction in thickness and thus weight is permissible. The sides and bottom can be made of substantially the same thickness and thus can be made of a single member. Therefore only one longitudinal joint along the bottom of the car is required resulting in inexpensive fabrication. Only one top chord is required to reinforce the unsupported edges of the curved side members. One or a limited number of transversely extending reinforcing members may be provided, if desired, particularly on long cars.

35 Claims, 8 Drawing Figures PIWEB 3.841.236

sum 20? a PAIENIEB w 1 511m FIG. 4.

FIG. 5.

FIG. 6.

CONTOUR UNDERGROUND MINE CAR BACKGROUND OF THE INVENTION This invention relates to underground mine cars.

Dimensions are very restricted in underground mine cars, particularly height and width. It is desired to utilize as much of this mine tunnel cross section as possible for lading carrying capacity.

Conventional underground mine cars usually include vertical strengthening members along the longitudinal length on the sides of the car. US. Pat. No. 2,859,709 directed to an ore mine car, and US. Pat. No. 3,240,168 and Canadian Pat. No. 887,966 directed to railroad gondola cars are illustrative of this general type of construction. See also Railway Locomotives and Cars, Nov. 1969, pages 26 and 27.

Cost is a very important factor in the marketability of the car. One of the main factors affecting the cost of the car is the weight or amount of metal in the car. The vertical strengthening members in the above constructions increase the weight and hence the cost of the car. The strengthening members also increase the expense of manufacture in requiring numerous fittings and weldings. Furthermore, the weld joints are often a point of inception of corrosive attack.

One current commercial railroad car construction described and illustrated in Railway Locomotive and Cars, Jan. 1972, pages 23 and 24, is used in hauling coal but not as an underground mine car. The car has a curved bottom having a small radius and sides which are partially curved. The curved portions take lading stress in tension. The structure basically includes three members, a bottom member with a small radius welded to two side members which are curved with a large radius at the bottom and flat near the top. Longitudinal chord members are provided along the sides of the car and at the top.

However, this car requires two longitudinally running welds in the center portion, which is expensive. Furthermore, this car is not efficient in maximizing volumetric capacity due to the sharp curvature of the bottom portion of the car and providing two longitudinal chord members on each side of the car adds to the weight of the car and to fabrication expense.

One object of the present invention is to provide an underground mine car of reduced weight without significantly sacrificing strength, rigidity or wear resistance of the car.

It is another object of the present invention to provide a car which efficiently utilizes the space available in a mine tunnel as lading carrying volume of the car.

Another object of the present invention is to provide an underground mine car which is easily and inexpensively fabricated.

Another object is to provide an underground mine car which is resistant to corrosive attack.

Another object of the present invention is to provide an underground mine car which is readily drainable.

Other objects will be apparent from the following description and drawings.

THE DRAWINGS FIG. 1 is a perspective view of the underground mine car of the present invention;

FIG. 2 is a top view of the underground mine car of the present invention;

FIG. 3 is a side elevational view of the underground mine car according to the present invention;

FIG. 4 is a sectional view of the underground mine car according to the present invention along the line 4-4 in FIG. 2; v

FIG. 5 is a sectional view of the underground mine car of the present invention along the line 5-5 of FIG.

FIG. 6 is a sectional view of the end portion of the underground mine car along the line 6-6 in FIG. 2;

FIG. 7 is a sectional view of the underground mine car of the present invention along the line 7-7 in FIG. 2;

FIG. 8 is an enlarged sectional view showing one type of longitudinal weld which may be used for the joint along the bottom of the car.

SUMMARY OF THE INVENTION In accordance with the present invention an underground mine car is provided in which the sides and bottom members are at least partly curved enabling these members to resist applied Iading forces primarily in tension rather than flexure according to prior construction. In addition, the curved sides transmit longitudinal loads (i.e. impact) more effectively than flat plate construction Of equal cross-sectional area. The radius of curvature is preferably from about 6 to feet for the sides and 10 to 30 feet for the bottom. This enables thinner sections to be utilized, and a reduction in car weight can be obtained. Since the number and extent of the welds is marketly reduced in the construction of the invention, and since such welds are often points of inception of corrosive attack, the structure is less susceptible to corrosion and hence this reduction in thickness and thus weight is permissible. Preferably the sides and bottom are made of substantially the same thickness and thus can be made of a single member. Therefore only one longitudinal weld of other appropriate joining means along the bottom of the car is required, resulting in inexpensive fabrication. Preferably only one chord is used as a longitudinal reinforcement for the sides of the car. One or a limited number of transversely extending reinforcing members may be provided, if desired, particularly on long cars.

DETAILED DESCRIPTION The underground mine car of the present invention is indicated generally at 10 in the drawing. The center portion 11 comprises spaced apart integral side and bottom members 12 and 14 which, if desired, may be made of a single piece of metal. The integral members 12 and 14 respectively comprise at least partly curved side portions 17, 19 and at least partly curved bottom portions 16 and 18. The general shape is shown in FIG. 4.

The radius of curvature of the side and bottom portions is a balance between curvature to increase strength and rectangularly to maximize mine tunnel cross section. The radius of curvature for the sides is preferably not more than about 60 feet depending upon car length to provide for strength and not less than about 6 feet to avoid excessive loss of lading capacity. At radii above about 60 feet the curvature of the sides approach a flat plate, requiring reinforcement on the side and bottom. At a radius less than about 6 feet loss of carrying capacity occurs at a greater rate than savings in weight and car cost. Limited portions of the side and/or bottom may have little curvature or be substantially flat, generally not exceeding about 25 percent of the side and/or bottom. If desired, a series of flat portions may be utilized which approximate a radius within the above range. Preferably the radius of curvature for the bottom is from acout 10 to about 30 feet to maximize both strength and carrying capacity.

The radius of curvature for the inward curve at the bottom is dictated primarily by that radius which is large enough to avoid excessive strain which may result in cracking. To this end the radius is preferably not less than about 3 inches. It is desirable to have the radius as small as possible preferably not above 10 inches to maximize lading capacity.

Bottom portions 16, 18 may have the same or a different radius of curvature than the side portions. Preferably, however, the radius of curvature of the side and bottom portions is substantially the same. For example, the side and bottom may be rolled to a desired radius of curvature and then bent to form the inward curve defining portions 16 and 18.

The height of the car is dictated by the height of the mine tunnel and may be as low as about 30 inches or as high as 5 feet or higher. The width of the car again is dictated by the width of the tunnel and, for example, may be from 6 feet to 8 feet.

Members 12 and 14 are welded or otherwise appropriately affixed together, such as by riveting, bolting, adhesive bonding, or a combination thereof, as indicated generally at 20 along the bottom portion of the car. For example, weld 20 may comprise, for example, a weld in which the members 12 and 14 are brought into close contact, for example, to /s inch and a weld support strip 22 tack welded to the two members along the length of the car body. Then the strip 22 is welded to respective bottom portions 16 and 18 of the members l2 and 14 as shown in FIG. 8.

Drain holes 106 are preferably provided in bottom portions 16 and 18. The curved sides 17 and 19 and curved bottom thus provide positive drainage.

The bottom portion of the car further comprises a channel 24 welded to the respective bottom portions 16 and 18 along the car and terminating adjacent vertical plates 26 and 28. Channel 24 provides longitudinal floor reinforcement. Openings 27 and 29 are cut in the bottom portions 16 and 18 and lug plates 30 and 32 are also provided therein adjacent plates 26 and 28, for example by welding. As shown in FIG. 3, the lug plates are provided so that lugs 34 mounted upon a conveyor 36 are movable about wheels 38 and 40 by an appropriate power source (not shown) and a cam surface 42 is provided to move lugs 34 into the locking position in engagement with the lug plates to engage the bottom of the cars and move them forward along the track to position them for dumping. The conveyor 36 and lugs 34 are shown schematically as their use and function are well known in the art.

End portions 46 and 48 are constructed similarly to the center portion of the car. Each integral members 47 and 49, if desired, may be made of a single piece of metal and comprise respectively the side portions 50 and 52, at least partly curved, and bottom portions 54 and 56, also at least partly curved. Similar ranges of radii of curvature may be used for the side and bottom curvature and for the bottom inward curve as are used in the center portion. The main difference is that the vertical extent of the side portions is considerably foreshortened. Integral members 47 and 49 are welded together at 58 with a weld similar to that shown in FIG. 8. Integral members 47 and 49 are preferably formed separately and buttwelded to center members 12 and 14.

End portions 46 and 48 are mounted upon suitable trucks 60 and 62 comprising wheels 64, 66, side bearings 68, 70, and springs 72, 74 (shown schematically in FIG. 5). Center plates 76 and 78 are mounted below stub sills and 77. Transversely extending body bolsters 80 and 82 (FIGS. 2 and 5) which extend below bottom portions 54 and 56 and are affixed to side portions 50 and 52 to transmit lading loads from the side members to the trucks 60-62. Each end portion is provided with a body side bearing 84, 86 which may comprise, for example, angles 88, 90 having mounted thereon steel plates 92 and 94.

End plates 96 and 98 are welded to integral members 47 and 49, both to the bottom portions 54 and 56 and to side portions 50, 52. Mounted upon the end plates 96 and 98 respectively are chords 100, 102 of a channel section as shown in FIG. 6 comprising channel member 104. Along the sides of the car members 13 and 15 which may, for example, have a cross section as shown in FIG. 7, are provided which extend through the end portions 46 and 48 as indicated at 51 and 53. End portions 51 and 53 are preferably welded to chords and 102.

Gussets 108 and 110 preferably are also provided and are welded in place to the car sides and to plates 26 and 28 respectively. The gussets help to maintain the curvature in the preformed shape.

Additionally, if desired, one or a limited number of transverse plates 112 may be provided to support integral members 12 and 14 and maintain rigidity. The plates 112 are welded to members 12, 14 and optionally to channel 24. In general, if used at all, one or at most two or three such members would be provided. It is desirable to minimize the number of such transverse members to minimize weight, fabrication time, and avoid weld joints where corrosion may begin.

Strength and rigidity is obtained through the use of the curved sides and curved bottom. The chords along the side and end portions of the car provide additional strength and rigidity. Thus, less weight per unit strength is obtainable with the construction of the present invention.

Through the use of the curved sides and bottom the longitudinal forces (impacts) on the car are more effectively taken and a thickness reduction from the usual 5/ l6 inch or greater to below 5 inch, preferably about 7/32 inch, can be realized without the loss of strength and rigidity. For example, a thickness reduction of 10 to 40 percent can often be obtained, which results roughly in a corresponding weight reduction in the car body, excluding trucks and draft gear.

The radius of curvature of the center and side portions and the inward curve at the bottom are such that the car volume to mine volume ratio is maximized and only about 10 percent of available mine volume is lost due to the curved sides corresponding to approximately 6 feet radius. Most preferably not more than about 5 percent is lost corresponding to approximately 14 radius. Furthermore, the simplified design with a single longitudinal weld reduces fabrication time and thus reduces labor cost.

The underground mine car is preferably made of corrosion resistant steel, for example of COR-TEN a registered trademark of U.S. Steel Corp., having a composition of C 0.12 max, Mn 0.20-0.50, P 0.07-0.15, Si 0.25-0.75, Cu 0.25-0.55, Cr 0.30-1.25, S 0.05 max, Ni 0.65 max.

Through the use of an appropriate corrosion resistant, low cost steel, little or no loss of corrosion and wear resistance results from the design of the present invention. In fact, fewer welded joints avoid points for the conception of corrosive attack, thus improved corrosion resistance may be observed with the design of the present invention.

What is claimed is:

1. An underground mine car comprising: opposite end sections supported by railway car trucks, and a center section having a bottom portion extending into the space between said trucks,

said center section comprising spaced apart integral center members comprising an at least partly curved side portion having a radius of curvature within the range of from about 6 to 60 feet and an at least partly curved bottom portion having a radius of curvature within the range of from about to 30 feet; each of said spaced integral center members having a bottom inward curve with a radius of curvature of at least about three inches; said spaced integral center members being joined together along their respective bottom portions; said opposite end portions comprising spaced apart integral end members comprising an at least partly curved side portion having a radius of curvature within the range of from about 6 to about 60 feet; and an at least partly curved bottom portion having a radius of curvature within the range of from about 10 to 30 feet; each of said spaced integral end members having a bottom inward curve having a radius of curvature of at least about 3 inches; said integral end members at each end being joined together along their respective bottom portions;

at each end of the car a generally vertical end plate extending transversely between said spaced apart integral end members; spaced apart generally vertical joining plates joining the bottom portions of said center section with the bottom portions of said end sections, said joining plates extending transversely between said spaced apart integral center members; chord extending longitudinally along each side of the car affixed to said curved side portions on said integral central members and to said curved side portions on said integral end members; whereby lading loads applied to said center and/or end members are resisted primarily in tension, and whereby the car volume to mine volume ratio is maximized without overstressing the inward curve between the side and bottom portion of said center and end members.

2. An underground mine car according to claim 1 wherein at least one of said at least partly curved side portions in said center section comprises a series of flat portions approximating a radius of curvature within the ranges of from about 6 to 60 feet.

3. An underground mine car according to claim 1 wherein at least one of said at least partly curved bottom portions in said center section comprises a series of flat portions approximating a radius of curvature of within the range of from about 10 to 30 feet.

4. An underground mine car according to claim 1 wherein at least one of said at least partly curved side portions in at least one of said end sections comprises a series of flat portions approximating a radius of curvature of within the range of from about 6 to 60 feet.

5. An underground mine car according to claim 1 wherein at least one of said at least partly curved bottom portions in at least one of said end sections comprises a series of flat portions approximating a radius of curvature of within the range of from about 10 to 30 feet.

6. An underground mine car according to claim 1 wherein the spaced integral members in said center section and in said end sections are joined together by a generally longitudinally running weld.

7. An underground mine car according to claim 1 wherein said spaced integral center members have a thickness not exceeding about A inch.

8. An underground mine car according to claim 7 wherein said spaced integral end members have a thickness not exceeding about A inch.

9. An underground mine car according to claim 8 wherein the inward curve at the bottom portion of said spaced integral center members has a radius of curvature of at least from about 3 to about 10 inches.

10. An underground mine car according to claim 8 wherein said spaced integral center members are welded to said spaced integral end members.

11. An underground mine car according to claim 9 wherein the inward curve at the bottom portion of said spaced integral end members has a radius of curvature from about 3 to about 10 inches.

12. An underground mine car according to claim 11 wherein the side portions of said spaced integral center members have a radius of curvature from about 10 to 30 feet.

13. An underground mine car according to claim 12 wherein the side portions of said spaced integral end members have a radius of curvature from about 10 to 30 feet.

14. An underground mine car according to claim 11 wherein said car has a height of from about 2% to 5 feet.

15. An underground mine car according to claim 14 wherein said car has a width of less than about 8 feet.

16. An underground mine car according to claim 11 comprising a channel member extending longitudinally between said joining plates.

17. An underground mine car according to claim 16 wherein said channel is affixed to the respective bottom members of said spaced apart center members.

18. An underground mine car according to claim 17 wherein openings are provided in the bottom portion of at least one of said center members adjacent said joining plates.

19. An underground mine car according to claim 18 wherein transverse plates are provided in said openings and affixed to at least one of center bottom portions for engagement with unloading lugs.

20. An underground mine car according to claim 11 wherein a transversely extending chord is affixed to the upper portion of each of said end plates and joins the longitudinally extending chords on opposite sides of the car.

21. An underground mine car according to claim wherein a curved channel member extends transversely between, and is integral with said spaced apart end members.

22. An underground mine car according to claim 21 wherein a stub sill is affixed to said channel.

23. An underground mine car according to claim 22 wherein side bearings are provided on said truck and on the bottom surface of said end portions which engage each other at least during swaying of the car about the truck.

24. An underground mine car according to claim 22 wherein said truck is provided with side frames inboard of said side bearings.

25. An underground mine car according to claim 11 wherein at least one reinforcing member is provided extending in a transverse direction affixed to at least one of said center and end members. v

26. An underground mine caraccording to claim 25 wherein said reinforcing member joins the side portion of said center member with the side portion of said end members.

27. An underground mine car according to claim 26 wherein at least one reinforcing member extends transversely between said spaced apart center members and is affixed thereto.

28. An underground mine car according to claim 26 wherein the reinforcing members comprise gussets extending only part way into the car.

29. An underground mine car comprising:

opposite end sections supported by railway car trucks and a center section having a bottom portion extending into the space between said truck;

said center section comprising spaced apart integral center members comprising an at least partly curved side portion and an at least partly curved bottom portion each having a radius of curvature within the range of from about 10 to about 30 feet;

said integral center members having a bottom inward curve having a radius of curvature within the range of from about 3 to 10 inches; said spaced integral center members being joined together along their respective bottom portions by a generally longitudinally running weld;

said opposite end portions comprising spaced apart integral end members comprising an at least. partly curved side portion and an at least partly curved bottom portion each having a radius of curvature within the range of from about 10 to about 30 feet;

said integral end members having a bottom inward curve having a radius of curvature within the range of from about 3 to 10 inches;

the integral end members located at each end of the car being joined together along their respective bottom portions by a generally longitudinally running weld; generally vertical end plates at each end of the 'car extending transversely between the spaced apart integral end members;

spaced apart generally vertical joining plates joining the bottom portions of said center section with the bottom portions of said end sections, said joining plates extending transversely between said spaced apart integral center members;

a chord member extending longitudinally along each side of the car affixed to said curved side portions on said integral center members and to said curved side portions on said integral end members;

whereby lading loads applied to said center and end members are resisted primarily in tension, and whereby said center and end members maximize the car volume to mine volume ratio without overstressing the inward curve between the side and bottom portions of said center and end members.

30. An underground mine car according to claim 29 wherein at least one of said at least partly curved side portions in said center section comprises a series of flat portions approximating a radius of curvature of within the ranges of from about 10 to 30 feet.

31. An underground mine car according to claim 29 wherein at least one of said at least partly curved bottom portions in said center section comprises a series of flat portions approximating a radius of curvature of within the range of from about 10 to 30 feet.

32. An underground mine car according to claim 29 wherein at least one of said at least partly curved side portions in at leastone of least one end sections comprises a series of flat portions approximating a radius of curvature of within the range of from about 10 to 30 feet.

33. An underground mine car according to claim 29 wherein at least one of said at least partly curved bottom portions in at least one of said end sections comprises a series of flat portions approximating a radius of curvature of within the range of from about 10 to 30 feet.

34. An underground mine car comprising:

opposite end sections supported by railway car trucks and a center section having a bottom portion extending into the space between said truck;

said center section comprising spaced apart integral center members comprising an at least partly curved side portion and an at least partly curved bottom portion each having a radius of curvature within the range of from about l0 to about 30 feet; said integral center members having a bottom inward curve having a radius of curvature within the range of from about 3 to 10 inches; and a thickness not greater than about A inch, said spaced integral center members being joined together along their respective bottom portions by a generally longitudinally running weld;

said opposite end portions comprising spaced apart integral end members comprising an at least partly curved side portion and an at least partly curved bottom portion each having a radius of curvature within the range of from about 10 to about 30 feet; said integral end members having a bottom inward curve having a radius of curvature within the range of from about 3 to 10 inches and a thickness not greater than about A inch, the integral end members located at each end of the car being joined together along their respective bottom portions by a generally longitudinally running weld;

generally vertical end plates at each end of the car extending transversely between the spaced apart integral end members; spaced apart generally vertical joining plates joining the bottom portions of said center section with the bottom portions of said end sections, said joining plates extending transversely between said spaced apart integral center the car volume to mine volume ratio without overmembefs; stressing the inward curve between the side and a chord member extending longitudinally along each side of the car affixed to said curved side portions on said integral central members and to said curved 35 A d r di t 24 side portions on said integral end members; nun erg me car accor ng ocalm h b lading loads applied to Said center and wherein said side frames have openings having springs end members are resisted primarily in tension, and thefeln for hl nmg. whereby said center and end members maximize bottom portions of said center and end members.

'zg gg I'VINITED STATES PATENT OFFICE l CERTIFICATE OF CORRECTION new; No. '3 ,8n1,236 Dated October is, 1o7u Inventofl James C. Hammonds end Walter E. .O'Lee 'rv It is certified that error appears in the above-identified patent and that said Letters Patent' are hereby corrected as shown below:

' Column 4, line 66, "1 should be 1-4 Column 8, line. 24 hould be portions in at least one of said end sections com- Signed and sealed this 21st day of January-1975.

(SEAL) Attest: McCOY M. GIBSON-JR. c. MARSHALL DANN Attesting Officer I Commissioner of Patents 

1. An underground mine car comprising: opposite end sections supported by railway car trucks, and a center section having a bottom portion extending into the space between said trucks; said center section comprising spaced apart integral center members comprising an at least partly curved side portion having a radius of curvature within the range of from about 6 to 60 feet and an at least partly curved bottom portion having a radius of curvature within the range of from about 10 to 30 feet; each of said spaced integral center members having a bottom inward curve with a radius of curvature of at least about three inches; said spaced integral center members being joined together along their respective bottom portions; said opposite end portions comprising spaced apart integral end members comprising an at least partly curved side portion having a radius of curvature within the range of from about 6 to about 60 feet; and an at least partly curved bottom portion having a radius of curvature within the range of from about 10 to 30 feet; each of said spaced integral end members having a bottom inward curve having a radius of curvature of at least about 3 inches; said integral end members at each end being joined together along their respective bottom portions; at each end of the car a generally vertical end plate extending transversely between said spaced apart integral end members; spaced apart generally vertical joining plates joining the bottom portions of said center section with the bottom portions of said end sections, said joining plates extending transversely between said spaced apart integral center members; a chord extending longitudinally along each side of the car affixed to said curved side portions on said integral central members and to said curved side portions on said integral end members; whereby lading loads applied to said center and/or end members are resisted primarily in tension, and whereby the car volume to mine volume ratio is maximized without overstressing the inward curve between the side and bottom portion of said center and end members.
 2. An underground mine car according to claim 1 wherein at least one of said at least partly curved side portions in said center section comprises a series of flat portions approximating a radius of curvature within the ranges of from about 6 to 60 feet.
 3. An underground mine car according to claim 1 wherein at least one of said at least partly curved bottom portions in said center section comprises a series of flat portions approximating a radius of curvature of within the range of from about 10 to 30 feet.
 4. An underground mine car according to claim 1 wherein at least one of said at least partly curved side portions in at least one of said end sections comprises a series of flat portions approximating a radius of curvature of within the range of from about 6 to 60 feet.
 5. An underground mine car according to claim 1 wherein at least one of said at least partly curved bottom portions in at least one of said end sections comprises a series of flat portions approximating a radius of curvature of within the range of from about 10 to 30 feet.
 6. An underground mine car according to claim 1 wherein the spaced integral members in said center section and in said end sections are joined together by a generally longitudinally running weld.
 7. An underground mine car according to claim 1 wherein said spaced integral center members have a thickness not exceeding about 1/4 inch.
 8. An underground mine car according to claim 7 wherein said spaced integral end members have a thickness not exceeding about 1/4 inch.
 9. An underground mine car according to Claim 8 wherein the inward curve at the bottom portion of said spaced integral center members has a radius of curvature of at least from about 3 to about 10 inches.
 10. An underground mine car according to claim 8 wherein said spaced integral center members are welded to said spaced integral end members.
 11. An underground mine car according to claim 9 wherein the inward curve at the bottom portion of said spaced integral end members has a radius of curvature from about 3 to about 10 inches.
 12. An underground mine car according to claim 11 wherein the side portions of said spaced integral center members have a radius of curvature from about 10 to 30 feet.
 13. An underground mine car according to claim 12 wherein the side portions of said spaced integral end members have a radius of curvature from about 10 to 30 feet.
 14. An underground mine car according to claim 11 wherein said car has a height of from about 2 1/2 to 5 feet.
 15. An underground mine car according to claim 14 wherein said car has a width of less than about 8 feet.
 16. An underground mine car according to claim 11 comprising a channel member extending longitudinally between said joining plates.
 17. An underground mine car according to claim 16 wherein said channel is affixed to the respective bottom members of said spaced apart center members.
 18. An underground mine car according to claim 17 wherein openings are provided in the bottom portion of at least one of said center members adjacent said joining plates.
 19. An underground mine car according to claim 18 wherein transverse plates are provided in said openings and affixed to at least one of center bottom portions for engagement with unloading lugs.
 20. An underground mine car according to claim 11 wherein a transversely extending chord is affixed to the upper portion of each of said end plates and joins the longitudinally extending chords on opposite sides of the car.
 21. An underground mine car according to claim 20 wherein a curved channel member extends transversely between, and is integral with said spaced apart end members.
 22. An underground mine car according to claim 21 wherein a stub sill is affixed to said channel.
 23. An underground mine car according to claim 22 wherein side bearings are provided on said truck and on the bottom surface of said end portions which engage each other at least during swaying of the car about the truck.
 24. An underground mine car according to claim 22 wherein said truck is provided with side frames inboard of said side bearings.
 25. An underground mine car according to claim 11 wherein at least one reinforcing member is provided extending in a transverse direction affixed to at least one of said center and end members.
 26. An underground mine car according to claim 25 wherein said reinforcing member joins the side portion of said center member with the side portion of said end members.
 27. An underground mine car according to claim 26 wherein at least one reinforcing member extends transversely between said spaced apart center members and is affixed thereto.
 28. An underground mine car according to claim 26 wherein the reinforcing members comprise gussets extending only part way into the car.
 29. An underground mine car comprising: opposite end sections supported by railway car trucks and a center section having a bottom portion extending into the space between said truck; said center section comprising spaced apart integral center members comprising an at least partly curved side portion and an at least partly curved bottom portion each having a radius of curvature within the range of from about 10 to about 30 feet; said integral center members having a bottom inward curve having a radius of curvature within the range of from about 3 to 10 inches; said spaced integral center members being joined together along their respective bottom portions by a generalLy longitudinally running weld; said opposite end portions comprising spaced apart integral end members comprising an at least partly curved side portion and an at least partly curved bottom portion each having a radius of curvature within the range of from about 10 to about 30 feet; said integral end members having a bottom inward curve having a radius of curvature within the range of from about 3 to 10 inches; the integral end members located at each end of the car being joined together along their respective bottom portions by a generally longitudinally running weld; generally vertical end plates at each end of the car extending transversely between the spaced apart integral end members; spaced apart generally vertical joining plates joining the bottom portions of said center section with the bottom portions of said end sections, said joining plates extending transversely between said spaced apart integral center members; a chord member extending longitudinally along each side of the car affixed to said curved side portions on said integral center members and to said curved side portions on said integral end members; whereby lading loads applied to said center and end members are resisted primarily in tension, and whereby said center and end members maximize the car volume to mine volume ratio without overstressing the inward curve between the side and bottom portions of said center and end members.
 30. An underground mine car according to claim 29 wherein at least one of said at least partly curved side portions in said center section comprises a series of flat portions approximating a radius of curvature of within the ranges of from about 10 to 30 feet.
 31. An underground mine car according to claim 29 wherein at least one of said at least partly curved bottom portions in said center section comprises a series of flat portions approximating a radius of curvature of within the range of from about 10 to 30 feet.
 32. An underground mine car according to claim 29 wherein at least one of said at least partly curved side portions in at leastone of least one end sections comprises a series of flat portions approximating a radius of curvature of within the range of from about 10 to 30 feet.
 33. An underground mine car according to claim 29 wherein at least one of said at least partly curved bottom portions in at least one of said end sections comprises a series of flat portions approximating a radius of curvature of within the range of from about 10 to 30 feet.
 34. An underground mine car comprising: opposite end sections supported by railway car trucks and a center section having a bottom portion extending into the space between said truck; said center section comprising spaced apart integral center members comprising an at least partly curved side portion and an at least partly curved bottom portion each having a radius of curvature within the range of from about 10 to about 30 feet; said integral center members having a bottom inward curve having a radius of curvature within the range of from about 3 to 10 inches; and a thickness not greater than about 1/4 inch, said spaced integral center members being joined together along their respective bottom portions by a generally longitudinally running weld; said opposite end portions comprising spaced apart integral end members comprising an at least partly curved side portion and an at least partly curved bottom portion each having a radius of curvature within the range of from about 10 to about 30 feet; said integral end members having a bottom inward curve having a radius of curvature within the range of from about 3 to 10 inches and a thickness not greater than about 1/4 inch, the integral end members located at each end of the car being joined together along their respective bottom portions by a generally longitudinally running weld; generally Vertical end plates at each end of the car extending transversely between the spaced apart integral end members; spaced apart generally vertical joining plates joining the bottom portions of said center section with the bottom portions of said end sections, said joining plates extending transversely between said spaced apart integral center members; a chord member extending longitudinally along each side of the car affixed to said curved side portions on said integral central members and to said curved side portions on said integral end members; whereby lading loads applied to said center and end members are resisted primarily in tension, and whereby said center and end members maximize the car volume to mine volume ratio without overstressing the inward curve between the side and bottom portions of said center and end members.
 35. An underground mine car according to claim 24 wherein said side frames have openings having springs therein for cushioning. 